Back in 2013, inventor Benjamin Krempel came up with a novel way to keep your tires inflated to a consistent pounds per square inch (also known as "psi"). The PumpTire uses a built-in pumping mechanism and the motion of the wheel to inflate itself. The problem with the original product is that riders need to use Krempel's bulky tires, and when they wear down a whole new PumpTire is required.

Krempel's newest invention, the PumpTube, will allow riders to keep their preferred tires and enjoy self-inflating convenience by simply installing a fancy tube. The inner tube itself is connected to an outer pumping mechanism, which amounts to a thinner tube capable of storing a little bit of air. Air travels through the valve into the pumping mechanism which runs along the perimeter of the inner tube. The pressure applied to the tube when the bike is ridden forces air from the outer mechanism into the main inner tube, thus inflating the tire.

In this diagram, the outer beige strip represents the pumping mechanism, and the gray section represents the inner tube.

PumpTire

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As air is drawn from the pumping mechanism into the inner tube, a vacuum is created that draws more air through the one-way valve into the pumping mechanism. The valve stem has a dial on it that allows riders to set their desired psi level, preventing any more air from entering the system once your tires are where you want them.

The PumpTube has some of the same drawbacks as thick puncture-resistant tubes and tire-liners—there is more mass along the perimeter of the wheel slowing down your acceleration rate, and the excess rubber doesn't allow the tire to conform to the road or trail as well which impacts bike's handling.

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That said, the benefits seem more significant than simply adding more rubber to prevent a flat. All tubes leak a little, especially if your bike sits in the garage unridden for a rainy week or two. You might not notice a difference or think to top off your tubes, but a drop of five or ten psi could mean a pinch flat on your next ride. If the PumpTube works as well as advertised, it should self-inflate to your ideal psi after just a few minutes of riding.

You won't find the PumpTube in your local bike shop yet. The design is still being fine-tuned, and Krempel hopes to raise funding via Kickstarter to scale up production sometime next year. The design is intriguing, we just hope it proves a reliable alternative to a normal inner tube.